The gasket structure shown in the related applications, above identified, met an urgent need in the automobile industry for throttle body to intake manifold gaskets occasioned by the need to insulate between these two components of the carburetor due to increase in temperature and/or the need to minimize evaporative losses in the carburetor bowl. The gaskets incorporated an asbestos phenolic resin bushing insert at the bolt holes in combination with a vegetable fiberboard core in the body structures, and the gaskets proved very satisfactory in withstanding temperatures up to approximtely 400.degree. F.
With the advent of more anti-pollution devices being used in conjunction with automotive engines, the temperatures in the area of the carburetor intake manifold onto which the carburetor is normally mounted may now go as high as 500.degree./600.degree. F (approximately), with the expectation that, in some applications somewhat higher temperatures may be encountered in the future. In a large number of applications the maximum temperatures that the part discussed encounters, cover only a portion of the gasket or insulator, i.e., in the area where heating air or exhaust gases pass by or through the gasket or gasket insulator. These changing requirements necessitate an entirely new approach to the gasket structure to be used between the intake manifold and the carburetor since neither the asbestos phenolic resin bushings nor the gasket body referred to in the related applications will withstand these higher temperatures. Hand in hand with the temperature durability requirement is the torque retention requirement, which can be divided into two parts: (a) torque sufficient to obtain and maintain the seal in the total operating environment of the carburetor assembly and (b) torque sufficient to obtain and maintain carburetor securement in this total operating environment. The material structures used in the related applications tend to lose torque retention as temperatures rise, which was one reason for using the asbestos phenolic resin bushings. To satisfy both parts of the torque retention requirement it was necessary substantially to improve the torque retention required for sealing and also the torque retention required for securement since the bushings used in the related applications would tend to disintegrate due to heat destruction of the phenolic resin.
In stating temperature conditions, or limitations, as herein referred to, it is important to understand where the temperatures are recorded for test purposes and something of the nature of the heat problem as it relates both to durability of the part described, and the fact that it must serve, for the most part, both as a heat insulator and as a seal.
Test work over a period of years has included monitoring of temperatures at the intake manifold by using thermocouple probes inserted into the manifold and by attaching probes to the mounting bolts that clamp the throttle body to the intake manifold gasket, in a fashion similar to that used by Car Manufacturers in their tests. On one test car for example, recordings indicated a maximum temperature of approximately 425.degree. F during a high speed run with outside temperatures ranging from about 95.degree. to 97.degree. F. One manufacturer in testing a Single Bbl. throttle body to manifold gasket at its Proving Grounds, under conditions simulating the pulling of a trailer up a long slope on a hot day, recorded a maximum temperature of about 602.degree. F, with the temperature dropping off sharply after the heavy load condition was relieved. The same gasket was also tested under simulated conditions on a dynamometer stand, which resulted in a recording of 605.degree. F. In stating herein that a particular material will withstand for example, 600.degree. F continuous when clamped in gasket form in a carburetor assembly, we refer to its use in carburetor assemblies. This important point is made for the reason that when a gasket is made up in accordance with the aforementioned related gasket structures, clamping it up between heavy ground carbon steel blocks at automotive production clamp loads and heating these blocks from the bottom side by placing it on a hot plate with a thermocouple probe inserted in a small hole in the lower clamping plate for a sustained period of time(approximately 22 hours), the related material construction will completely fail. Conversely, the high temperature structure herein disclosed will withstand the temperature and function very satisfactorily, both as a gasket and as an insulator. This same gasket clamped up as above described and heated to approximately 300.degree. F maximum and held, will perform quite satisfactorily and match the after-test appearance and general physical properties of the after-test gasket removed from the test vehicle, which was checked out at 425.degree. F.
Not only is a carburetor assembly in a vehicle a sizeable heat sink, but when the carburetor is operating it has somewhat of a refrigeration effect due to the cooling effect of the fuel-air mixture circulating through the intake manifold in the nature of a relatively cold air blast. This combination heat with cool circulating air involved is the environment in which the part must live and for purposes of this disclosure is the base which we specifically refer to in speaking of temperature resistance. As an example of this a simulated "hot block" test of a single Bbl. gasket was conducted which performed satisfactorily at the 605 Deg. temperature referred to above, and like a similarly "hot blocked" sample of related material, both lost all the torque retention, charred and/or shrunk in thickness and the bushings having lost all their torque retention partially disintegrated. Having run numerous tests both on test vehicles and on "hot block" tests it has been possible to correlate and substantiate the fact that temperature durability using "hot blocks" tests, is conservatively 100.degree. to 150.degree. higher insofar as what the gasket actually encounters than that encountered in a vehicle. It is most important to understand this when discussing temperature durability.
There being a host of engine models and car models, each with standard or special features, it becomes impractical to conduct tests on every car -- from a gasket manufacturer's standpoint. However, this relatively simple "hot block" method has been developed and has been found to correlate very well with the many tests that the Car Manufacturers conduct for heat durability. Specifically, gaskets or gasket insulators that have been submitted for test come back with results that establish the heat durability along with the other environmental requirements.
The primary object of this invention, therefore, is to provide gasket structures suitable for these high temperature applications, although the improved structures may be used in lower temperature applications as well.